Distributed Transactions via Persistent Messaging Notion of a single transaction spanning multiple sites is inappropriate for many applications E.g.,transaction crossing an organizational boundary Latency of waiting for commit from remote site Alternative models carry out transactions by sending messages Code to handle messages must be carefully designed to ensure atomicity and durability properties for updates Isolation cannot be guaranteed,in that intermediate stages are visible,but code must ensure no inconsistent states result due to concurrency Persistent messaging systems are systems that provide transactional properties to messages Persistent messages are guaranteed to be delivered exactly once Database System Concepts-7th Edition 23.17 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 23.17 ©Silberschatz, Korth and Sudarshan th Edition Distributed Transactions via Persistent Messaging ▪ Notion of a single transaction spanning multiple sites is inappropriate for many applications • E.g., transaction crossing an organizational boundary • Latency of waiting for commit from remote site ▪ Alternative models carry out transactions by sending messages • Code to handle messages must be carefully designed to ensure atomicity and durability properties for updates ▪ Isolation cannot be guaranteed, in that intermediate stages are visible, but code must ensure no inconsistent states result due to concurrency • Persistent messaging systems are systems that provide transactional properties to messages ▪ Persistent messages are guaranteed to be delivered exactly once